专业英语八级题库_大学英语题库

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： teeth—tooth[解析] 名词直接作前置修饰语时，应该用单数形式。

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： count—account[解析] account和count由于形近容易混淆。account是“说明、认为”的意思，c...

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： (toll)from—on[解析] take one"s toll on somebody/something的意思是“...

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： written—writing[解析] written和writing都可以作定语修饰名词，written是指“书面的”...

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： saber-tooth—saber-toothed[解析] 如果是“形容词+名词”作前置修饰语，那么名词要加-ed词缀，...

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： bloody—blood[解析] bloody和blood都可以作为定语修饰名词，但是bloody的意思是“血腥的”，如...

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： ∧case—the[解析] in case of和in the case of的意思是不同的，前者的意思是“万一”，如：...

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： try—trying[解析] be analogous to的意思是“和……类似”，to是介词，后面跟名词或-ing分词...

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： must—may/can[解析] must的推测性用法表示“一定是、一定会”，说话者对所作出的推测十分有把握，一般来说，...

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： alters—altered[解析] 这里谈的是恐龙灭绝的时期，所以时间是过去。

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： loses—misses[解析] miss和lose的意思由于受到中文的影响而容易混淆，它们是有很大区别的。动词miss...

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： to(limit)—/[解析] but also和前面的not only构成并列结构，所以动词应该是不带to的不定式。

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： whales—whale[解析] “定冠词+可数名词的复数”是特指，所以the blue whales是特指，但是上下文...

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： On—By[解析] way的词组很多，要熟悉一些常用的词组。如：by way of(作为)，in the way(挡路)...

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： complete—total[解析] 原文的意思是“摄入的卡路里的总量”，表示数量上的总数应该用total，comple...

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： If—Even if[解析] 要理解两个分句的关系，句子的意思是即使有一部分信息丢失了，还是可以根据余下的部分重构图像，...

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： much—many[解析] as...as后面的名词是insects and animals，是可数名词，所以应该说as...

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： for—/[解析] seek是及物动词，直接跟宾语，要和look for区分开来。

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： For—As/Since[解析] 尽管for作为连词可以引导原因状语分句，但是它一般不放在句首，所以应该改成since或...

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： remains—remain[解析] 关系分句that remain的先行词是the parts of the plat...

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： concoct—concocting[解析] 动词concoct通过连词and和前面的modifying、searchi...

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： just—/或since—because[解析] 原因状语分句可以用because，since，as，for来引导，只有...

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： raining—rain[解析] (热带的)雨林应该表达为rain forest而不是raining forests。

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： already—yet[解析] 这是一个否定句，所以应该用yet。

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： and—but[解析] 前一个分句说这种比较是非常吸引人的，而后一个分句讲到人们对它的批评，所以前后是一个转折关系。

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： the—/[解析] East Africa是专有名词，大多数人名和地名的专有名词前不加定冠词。如：East China。...

填空题

Excessive calories from sugar can contribute to weight
problems, and sugar is also well known for its ability to
promote teeth decay. Too many calories from fat have also 1
taken their toll from the public"s health. In 1988, the U.S. 2
surgeon general issued a report linking high levels of fat intake
to an increased risk for obesity.
Obesity is a risk factor for high bloody pressure, stroke, 3
and diabetes. Research has also shown a relationship between
high levels of fat in the diet and cancer. In addition,
scientists have linked some types of fat to high blood cholesterol
levels, which must lead to heart disease. Such reports 4
have prompted health experts and nutritionists to recommend
that adults and children over age 2 not only watch
their sugar intake but also to limit their fat intake to a 5
maximum of 30% of their complete calories. This has encouraged 6
many people to turn to products made with fat and
sugar substitutes. Low-calorie sugar substitutes have been
around for decades, but the recent trend in eating "light" has
created a boom in this branch of food-technology research.
Today, food chemists are seeking for better substitutes by 7
modifying existing foods, searching for new compounds
in nature, and concoct entirely new substances. But the 8
research process is complicated by our incomplete understanding
of how the human body interacts with the chemicals
we eat.
For example, scientists do not already know exactly 9
why some substances taste sweet. Other questions involve
the safe and usefulness of artificial fats and sweeteners. 10

答案： safe—safety[解析] safe是形容词，它作为名词的意思是“保险箱”，所以应该改成safety。

填空题

Several analogies have been used to explain human
memory, the construct used to count for the way one 11
experiences at one point in time influence behavior at a later
point in time. Plato, for example, suggested memory was
analogous to the impression of messages on wax written 12
tablets. For Plato, writing on the tablet represented learning
something new. The tablet itself was the memory store, and
reading the tablets later was analogous to try to recall the 13
stored information. Like the writing on a wax surface, with
the passing of time, memories became less clear. Unfortunately,
Plato"s analogy loses an important characteristic of 14
memory, namely that it is selective. On way of contrast, one 15
always has access to the information on the tablet, unless
all or part of it is destroyed. Another analogy is of memory
and a hologram. A hologram is a device which stores a
three dimensional record of a scene using photography with
a laser light. If part of the holographic plate is missing, it is 16
possible to reconstruct the image with the parts of the plate
that remains. Experiences or knowledge can also be recalled 17
using incomplete memories. Other analogies involve artificial
methods of storing information, too. The comparison of
the mind to a computer is attractive just since it emphasizes 18
the ability of human memory to recall information quickly,
and the same objection stated above with regard to Plato"s 19
hypothesis apply to here. 20

答案： (apply)to—/[解析] apply在这里是“适用”的意思，如果后面是名词，那么应该说apply to somet...

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： living—alive[解析] remain是系动词，后面的形容词是主语补足语，living不能作主语补足语，应该改成...

填空题

Dinosaurs, saber-tooth tigers and the dodo bird are 31
famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic 32
event alters the global climate enough to lead to their 33
disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American 34
bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food. 35
Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the 36
clearing of more land, habitats such as raining forests and 37
grasslands disappear.
In the East Africa, once renowned for its wildlife, few 38
wild animals remain living outside the boundaries of 39
national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland 40
areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.

答案： clearing—cleared[解析] clear作为动词有“扫除(障碍)”这个意思，这时它是及物动词，如：The f...

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： grew—grow[解析] 这里说的是发展中国家的现状，所以应该用一般现在时。

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： that—those[解析] 代词that的先行词是populations，是复数，所以应该改成those。

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： alive—live[解析] 破折号后面的内容解释crude birth-rate，是每一千人中活的出生人口，那么bir...

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： it—there[解析] that后面是一个存在句，所以应该把it改成there。

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： futile—fertile[解析] futile和fertile混淆的话，意思就完全不对了。前者是“无用的、没有结果的...

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： having—have[解析] an incentive to的意思是“有(做某事的)动力”，to为不定式符号，后接动词...

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： mean—means[解析] 虽然主语more children看起来是复数，但是这只表示一个现象“孩子多”，在意义上是...

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： make—makes[解析] 尽管主语是a high life expectancy coupled with a hi...

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： and∧—that[解析] 分句societies should work for zero population gr...

填空题

One major obstacle to economic development is population
growth. The populations of most developing countries grew 21
at a rate much faster than that of industrialized countries. 22
One reason for this growth is the high crude birth-rate—the
number of alive births per 1,000 people. In some developing 23
countries, the population is so large that it is barely enough 24
futile land and other resources to support it. Many less 25
developed countries depend extensively on agriculture, adding
to the problem. In these countries, an incentive to having 26
many children exists. Most farms are worked by families,
and children can work in the fields at an early age. More
children mean more workers. In addition, having many children 27
ensures the parents that someone will look after them
in their old age. Another problem for developing countries is
increasing life expectancy—the average remaining lifetime
for persons who reach a certain age. Better education, international
aid, and emphasis on health-care facilities help people
live longer. A high life expectancy coupled with a high
crude birthrate make it difficult to increase per capita GNP. 28
Finally, people have different views on what is the proper
rate of population growth. Some feel that the earth is too
crowded already and societies should work for zero population 29
growth—the condition in which the average number of
births and deaths balances so that a population stops growing. 30
Others feel that population growth is a natural event and
that efforts to disrupt it are morally and religiously wrong.

答案： balances—balance[解析] 这一题有一定难度。主语是the average number of birth...

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